Various devices for forming fluid cushions or fluid bearings have been used for the contactless support of a web as the latter changes directions during its course of travel. These running webs may be required to pass through a number of different processes or directed in different directions. By way of example, webs resulting from a papermaking process may be directed through contactless supporting devices to downstream converting operations to produce absorbent paper products such as diapers, facial tissues, and the like. Such contactless support devices are described as generally partially cylindrical surfaces through which pressurized air is introduced through various slots, holes, apertures, or the like.
However, it should be realized that web materials handled under such processes are generally planar with a thickness much smaller than the dimensions of the material. Such webs are likely to include paper, cloth, plastic film, woven, non-woven, and metal films. These web materials are known to present unique process challenges. For example, it is known that typical flexible web materials are easily damaged, and can result in final products that are unacceptable.
Such thin materials that are produced into wound webs are also known to have fluctuations in the wound web tension throughout the length and width of the web. Such fluctuations can be problematic as the web is unwound and transported by processing equipment during the conversion of large rolls of web material into finished products. Such web tension fluctuations may result in wrinkled, broken webs, webs of varying widths, a loss of control of the web material during processing, and ultimately provide for a loss of quality and/or productivity.
Thus, in most applications, it is desirable, if not imperative, to keep the web material from coming into direct contact with handling surfaces. The web material may be recently imprinted, and, thereby, carrying a wet image on at least one surface. Alternatively, the web material may be delicate and have a relatively low basis weight. Yet still, the web material may be wet. Therefore, preventing contact of the web material with a control surface can be beneficial, for example, if the control surface is dirty or greasy. Additionally, mechanical flaws in the surface of conventional control systems may cut or severely scar the surface of the web material. Further, it can be difficult to provide conventional web handling equipment to be surface speed matched to the speed of the web. This can be especially true if the process requires the web material speed to be variable, or if velocity fluctuations are caused by out of round or non-uniform supply rolls.
Additionally, moving and/or tensioned web materials may have inherent properties that provide additional difficulty in handling. For example, a material may have a lateral contraction when the material is subjected to an applied elongation. Such lateral contraction in a tensioned web material is known as the “Poisson lateral contraction effect.” Also, it has been seen that the stress and/or strain characteristics of the web material may vary laterally to a considerable extent. This may cause one portion of the web substrate to be tight and another portion of the web substrate to be loose. Additionally, low basis weight materials, because of their ability to stretch, can easily become wrinkled as the unconstrained web material moves over traditional supports. This can lead to wrinkles in the finished product. Typically, wrinkles can lower the product functionality by reducing absorbency of cellulose-based web materials and detract from the appearance of the finished product if it is formed from tissue paper.
Previous air-driven web handling equipment has been provided to frictionlessly, aerodynamically, and/or hydrodynamically support a moving web material on a cushion of fluid, such as air or gas, as the moving web passes over the control surface. Such devices are described in U.S. Pat. Nos. 4,043,495; 4,197,972; 5,775,623; 6,004,432; and 6,505,792. However, such devices as described do not reduce the Poisson lateral contraction that inherently occurs in a moving and/or tensioned web material as it passes through a converting process. Additionally, it is possible for these described devices to utilize excessive air flows. Excessive air flow can cause loss of control of the web material due to excessive lift. Further, the described devices do not provide the ability to remove dust generated by the moving web material.
Therefore, a device that provides contactless support of a moving web material that is capable of reducing the Poisson lateral contraction in a moving and/or tensioned web material is required. Such a device would be capable of controlling or turning a web material without wrinkling or significant stretching. Further, it is also a benefit to be able to provide such a device with the ability to remove dust from the web material as the web material progress through a web handling or converting process.